Lead pollution at firing ranges has been a problem for a number of years. Because of current interest in the reduction of lead pollution, correction of this problem has become more important in recent years. There are several sources of lead at these firing ranges. Ordinary primers which are used in conventional ammunition to activate the ammunition's explosive charge or propellant, contain lead styphnate which is propelled into the air as a particulate. The lead bullet or projectile itself also contributes significantly to lead pollution from several mechanisms inherent in the firing process. The heat created from the explosion of the ammunition's propellant upon firing, melts minute quantities of the lead in the bullet or projectile which is propelled out of the barrel of the gun and solidifies into microscopic particulates. The friction between the lead bullet or projectile and the gun barrel creates additional lead particulate through abrasion. When the bullet or projectile strikes the back stop or other restraining mechanism at the firing range, the bullet or projectile is broken or otherwise disintegrates from the impact, resulting in additional lead particulate accumulation.
The United States government, particularly the agencies involved in monitoring safety conditions, has set extremely restrictive standards governing the amount of airborne lead particulate which can be generated at firing ranges. As a result of the imposition of these standards, many ranges have been forced to install expensive ventilation and filtration systems, or to cease operations entirely. Restrictive standards have also been implemented governing the presence of lead in earthen butts typically associated with outdoor firing ranges. Through exposure to rain, lead can leach into underground water tables, thereby causing drinking water problems. As a result, outdoor ranges are being forced to excavate this lead and dispose it as well as all of the lead-contaminated earth disposed of in accordance with regulations dealing with the safe handling, transportation and disposal of hazardous materials.
Prior attempts have been made to solve this problem through the use of non-lead alternative metals, e.g., copper, bismuth etc., and loading the ammunition with lead-free primers. This solution however creates its own problems. Typically, the solid copper rounds cause more damage to the back stop of the range, and also have a greater tendency to ricochet and splash back, with attendant safety hazards. In the case of bismuth, the high costs of the material makes it a viable alterative only when the substantially higher cost of the round is no object.
There have been a number of other efforts in the prior art to alleviate the problem of lead pollution at firing ranges. One such attempt is disclosed in U.S. Pat. No. 2,995,090 to Daubenspeck who teaches the manufacture of a gallery bullet using a thermoplastic binder to adhere iron powder into a solid bullet body. Daubenspeck's bullet was made by dissolving the plastic binder in a solvent and mixing the plastic solvent solution with metal powder to coat the individual particles of the powder. The coated particles are then cold-molded into a bullet and baked at a temperature of about 100.degree. F. above the softening point of the plastic binder to complete the internal bonding of the cold-molded bullet. The Daubenspeck technique does not provide adequate structural strength to the resulting product to provide consistent firing results. Bullets made according to this process lack sufficient weight and/or specific gravity to enable the bullets to mirror a live ammunition round of similar size and caliber.
In U.S. Pat. No. 3,570,406 issued to Steyerberg et al., another alternative is taught wherein the loose bulk granular filing is coated with a synthetic jacket. The jacket either disintegrates upon firing or upon impact. The Steyerberg bullet however, does not provide the strength and accuracy of the bullet of applicant's invention. Other proposed solutions have involved the use of various thermoplastics in conjunction with various types of metal fillers. European Patent Disclosure EP-A-0 096 617 to Societe Francaise de Munitions (SFM) describes a training bullet having a mixture of nylon, a powder of a ductile material and a solid lubricant. This disclosure describes a practice ammunition wherein the specific gravity of the compound is between 3 and 5.
World Intellectual Property Organization Publication 88-09476 describes a bullet comprised of a matrix of plastics having a water absorption factor similar to or greater than that of nylon-11 and containing a filler to raise the specific gravity to 3-7. The preferred plastic material was nylon-6 or nylon-6,6 and the filler material was a finely divided metal, preferably a mixture of copper, bronze or tungsten.
U.S. Pat. No. 5,237,930 to Belanger et al., proposes an ammunition comprising a compacted mixture of fine copper powder and a thermoplastic resin selected from the group consisting of nylon-11 and nylon-12. The mixture, which is compacted by injection molding, has at least 90% by weight of copper and a minimum specific gravity of 5.7.
The applicant has utilized other nylons, such as Nylon 6/12 in prior frangible bullet formulations.
Such prior art techniques have, in some cases, reduced lead pollution at ranges. Others have eliminated lead pollution, but have created other problems such as excessive wear and safety hazards from splash back and ricochet. While the solutions of SFM, Booth and Belanger have eliminated lead in the projectile, their resulting projectiles have far less weight and mass than that of the conventional ammunition they are intended to mimic. This factor causes two significant problems. First, the weight of this prior art frangible ammunition is insufficient to cycle properly in the autoloaders used by many shooters. Second, the insufficient weight contributes to a projectile trajectory which is significantly different than conventional ammunition of similar caliber, making the practice ammunition an inadequate substitute for the live round. To compensate for the lack of weight and/or mass, manufacturers have attempted to increase the amount of propellant contained in each round in an effort to propel the projectile at a higher speed thereby producing a trajectory path more closely matching the counterpart live round. However, a consequence of these higher propellant loadings is an increased chamber pressure in the firearm which can in some cases, come dangerously close to the maximum limitation allowable under SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) guidelines, creating potential hazards in weapons that may be worn or stressed and thus, susceptible to rupture and fragmentation from these higher chamber pressures.
In light of the deficiencies noted in the prior art, a new alternative frangible practice ammunition is presented which more closely approximates the firing characteristics of live ammunition than has heretofore been possible.